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Performance analysis of OFDM communication systems

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5 pages
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  1. Abstract
  2. Introduction
  3. Block diagram of overall system
  4. Comparison with CDMA
  5. Stimulation results
  6. Definition of multi-antena OFDM systems
  7. Results and conclusion
  8. References

Today life does not seem possible without wireless in some form or the other. The demands on bandwidth and spectral availability are endless. Consequently, wireless designers face an uphill task of limited availability of radio frequency spectrum and complex time varying problems in the wireless channel, such as fading and multipath, as well as meeting the demand for high data rates. Simultaneously, there is an urgent need for better quality of service (QoS). Orthogonal Frequency Division Multiple Access (OFDMA) is a promising technique for broadband wireless communication because it can combat inter-symbol interference (ISI) caused by the dispersive fading of wireless channels. OFDMA is a multi-user version of the popular OFDM digital modulation scheme. This paper is one of the footsteps towards technical contribution in the world of wireless communication. OFDM's subcarriers make it very conducive to other technologies, such as multiple input-multiple-output(MIMO) antenna implementations, as well as multiple access (OFDMA) implementations.

[...] In the third phase, various designs and techniques for the improvement of the performance is carried out focusing TABLE 1 SHORT HISTORY OF WIRELESS COMMUNICATION on multi antenna OFDM systems. Performance comparison with other techniques is also done and stressed upon INTRODUCTION The origins of OFDM development started in the late 1960's with the introduction of Frequency Division Multiplexing (FDM) for data communications. In 1966 Chang patented the structure of OFDM and published the concept of using orthogonal overlapping multi-tone signals for data communications. [...]


[...] Figure-5 OFDM Waveform in Time Domain Two Branch Transmit Diversity with Two Receivers It is possible to provide a diversity order of 2M with two transmit and M receive antennas. Figure 9 Two Branch Transmit Diversity Scheme with two Receivers Figure 7 Two Branch Transmit diversity scheme with one receiver Note that an increase in transmit diversity improves the Here, for simulation, parameters taken are Number of Symbol pairs to be transmitted 1000 Modulation Scheme BPSK performance. This is a very important inference from a commercial point of view, because handheld mobiles always pose a lot of problems in achieving antenna diversity at the receiver. [...]


[...] In other words, using two antennas at the transmitter, the scheme doubles the diversity order of systems with one transmit and multiple receive antennas. No feedback from receiver to transmitter is required for CSI to obtain full transmit diversity Low complexity decoders. No bandwidth expansion (as redundancy is applied in space across multiple antennas, not in time or frequency). No need for complete redesign of existing systems to incorporate this diversity scheme. Hence, it is very popular candidate for improving link quality based on dual transmit antenna techniques, without any drastic system modifications. [...]

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